This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Tris(dithiolene) transition metal complexes have piqued considerable interest in inorganic chemistry due to their fascinating physical properties and electronic structures. Moreover, tris(dithiolene) complexes were the first discrete molecules to possess trigonal prismatic geometry, a feature observed in the oxidized active sites of several molybdenum and tungsten enzymes that catalyze a wide variety of fundamental biochemical reactions. In material sciences, certain dithiolene complexes are candidate materials for nonlinear optical devices and laser applications due to their enormous absorption bands in the near-infrared region. Their reversible redox chemistry has been utilized in the production of semi- and superconducting materials and sensors. The understanding of enzymatic reaction mechanisms or the design of new functional materials should be based on a thorough understanding of the electronic structures of such compounds. Dithiolene ligands can exist as radicals and diradicals and are described as ?non-innocent?, which makes the oxidation and spin states of the central metal ambiguous and difficult to determine experimentally. The existence of oxidized diselenolene ligands is still unknown. Thus, x-ray absorption spectroscopy at the metal K-, and L-edges as well as the sulfur and selenium K-edges is ideally suited to provide fundamental electronic structure insights into the function of these systems. Additionally, metal and ligand EXAFS will assist in defining metric parameters in the solid and solution state. Sulfur and selenium EXAFS are perfectly poised to gauge the geometric change from trigonal prismatic to octahedral as the complex is sequentially reduced by measuring interligand distances. The experiments will be combined with quasi-relativistic density functional as well as multiplet calculations in order to obtain more insight into the experimental data.